As EQ said, it sounds like your system is overloaded. Now this can be managable to some extent, increasing the total water volume of the system, a sump/refugium with macroalgaes for additional nutrient export, additional live rock to increase the amount of surface area for nitrifying bacteria.... Right now frequent water changes will help, but will not resolve the problem by itself.

Hope this helps a bit, keep us posted of your methods and any results.